1. Field of the Invention
This invention relates to an optical system for image rotation comprising two Pechan prisms located on an optical axis and a lens system located on the same optical axis, whereby the two Pechan prisms can be rotated relative to each other around the optical axis.
2. Description of Related Art
A similar optical system is described in W087/07391. This system is designed to be used in the printing industry, where under certain conditions it is necessary to rotate an image by 90.degree.. In this system, one of the two Pechan prisms is located in the air space between an 8-lens image-reversing lens system and its subject plane, and the other Pechan prism is located in the air space between the lens system and its focal plane.
The optical system of the prior art has the disadvantage that the Pechan prisms must be made of expensive, heavy and highly refractive glass, the refractive index of which is on the order of magnitude of 1.73 to 1.76.
The present invention provides an optical system of the type described above that is both lighter in weight and more economical to manufacture than similar systems of the prior art.